The invention relates to a method of manufacturing an optically scannable information carrier, which method comprises a first step wherein a master mold is manufactured, and a second step wherein, by means of the master mold or by means of a daughter mold manufactured by means of said master mold, the information carrier is manufactured by means of a replica process, in which first step a photosensitive layer provided on a substrate is irradiated by means of a modulated radiation beam which is focused to a scanning spot on the photosensitive layer by means of an optical lens system, the substrate and the lens system being moved relatively to each other, and a liquid being provided in a gap which is present between the photosensitive layer and a lens of the lens system facing said photosensitive layer.
The invention further relates to a method of manufacturing a master mold, which is used in the manufacture of an optically scannable information carrier, according to which method, a photosensitive layer provided on a substrate is irradiated by means of a modulated radiation beam which is focused to a scanning spot on the photosensitive layer by means of an optical lens system, the substrate and the lens system being moved relatively to each other, and a liquid being provided in a gap which is present between the photosensitive layer and a lens of the lens system facing said photosensitive layer.
The invention also relates to a device for the manufacture of a master mold, which is used in the manufacture of an optically scannable information carrier, which device is provided with a table which can be rotated about an axis of rotation, on which table a substrate with a photosensitive layer can be placed, and with a radiation source, an optical lens system for focusing a radiation beam generated in operation by the radiation source to a scanning spot on the photosensitive layer, a displacement device by means of which the lens system can be displaced with respect to the axis of rotation mainly in a radial direction, and a liquid supply means for providing a liquid in a gap between the photosensitive layer and a lens of the lens system facing said photosensitive layer.
A method and a device, of the types mentioned in the opening paragraphs, for the manufacture of a master mold are disclosed in JP-A-10255319. In accordance with the known method, a photosensitive layer is applied to a disc-shaped substrate made from glass. The substrate is secured onto a table of the known device. The table and the substrate are rotated about an axis of rotation extending perpendicularly to the substrate, and the lens system is displaced, at a comparatively low rate, in a radial direction with respect to the axis of rotation, so that the scanning spot of the radiation beam formed on the photosensitive layer follows a spiral-shaped track on the photosensitive layer. The radiation beam, which is a laser beam in the known device, is modulated such that a series of irradiated and non-irradiated elements is formed on the spiral-shaped track, which series correspond to a desired series of information elements on the information carrier to be manufactured. The photosensitive layer is subsequently developed, so that the irradiated elements are dissolved and a series of depressions are formed in the photosensitive layer. Next, a comparatively thin aluminum layer is sputtered onto the photosensitive layer, which aluminum layer is subsequently provided with a comparatively thick nickel layer by means of an electrodeposition process. The nickel layer thus formed is subsequently removed from the substrate and forms the master mold to be manufactured, which is provided, in the manner described above, with a disc-shaped surface having a series of raised portions corresponding to the desired series of information elements on the information carrier to be manufactured. The master mold thus manufactured can suitably be used in the manufacture of the desired information carriers, however, in general, a number of copies, so-called daughter molds are made by means of the master mold in a replica process. These daughter molds are used to manufacture the desired information carriers by means of a further replica process, generally an injection molding process. In this manner, the required number of master molds, which are comparatively expensive, is limited. Such a method of manufacturing an optically scannable information carrier, such as a CD or DVD, having pit-shaped information elements by means of a master mold or by means of a daughter mold manufactured by means of said master mold is commonly known and customary.
In accordance with the known method, the gap present between the photosensitive layer and the lens of the lens system facing said photosensitive layer is filled with water. For this purpose, the known device is provided with an outflow opening, which is situated near the axis of rotation of the table. The water supplied via the outflow opening is spread, under the influence of centrifugal forces, substantially throughout the surface of the photosensitive layer, so that also said gap is filled with water. Since water has a considerably larger optical refractive index than air, the provision of water in said gap leads to a substantial increase of an angle which the rays originating from the radiation beam and the optical axis of the lens system include at the location of the scanning spot. As a result, the scanning spot of the radiation beam on the photosensitive layer is reduced considerably, so that a much larger number of irradiated and non-irradiated elements can be formed on the photosensitive layer, and the information carrier to be manufactured has a higher information density.
A drawback of the known method and the known device resides in that the liquid film formed in said gap is not always homogenous as a result of air inclusions in said liquid film. As a result, impermissible faults develop in the photosensitive layer. In addition, the inhomogeneous liquid film exerts varying forces on the lens system. Since the lens system can be displaced in directions perpendicular and parallel to the photosensitive layer by means of an actuator to focus and position the radiation beam on the photosensitive layer, and this actuator has a limited rigidity in said directions, the varying forces exerted by the liquid film cause undesirable vibrations of the lens system in said directions, which may also lead to impermissible faults in the photosensitive layer. A further drawback of the known method and the known device resides in that a comparatively large quantity of liquid must be supplied. As a result, the known device must be provided with extensive measures to preclude undesirable contact between the liquid and other parts of the device.
It is an object of the invention to provide a method of manufacturing an optically scannable information carrier, a method of manufacturing a master mold, and a device for the manufacture of a master mold of the types mentioned in the opening paragraphs, wherein the above-mentioned drawbacks of the known method and the known device are precluded as much as possible.
To achieve this, a method in accordance with the invention for the manufacture of an optically scannable information carrier and a method in accordance with the invention for the manufacture of a master mold are characterized in that the liquid is provided via an outflow opening which, viewed in a displacement direction of the substrate at the location of the scanning spot relative to the lens system, is situated upstream from the scanning spot and directly adjacent said lens, said outflow opening being provided in a wall, which substantially extends in an imaginary plane wherein a side of the lens facing the photosensitive layer extends.
To achieve this object, a device in accordance with the invention for the manufacture of a master mold is characterized in that the liquid supply means comprises an outflow opening which, viewed in a tangential direction with respect to the axis of rotation, is situated upstream from the optical axis and directly adjacent said lens, said outflow opening being situated in a wall, which substantially extends in an imaginary plane wherein a side of the lens facing the photosensitive layer extends.
As the outflow opening is situated, viewed in the displacement direction of the substrate with respect to the lens system, upstream from the scanning spot, the liquid is transported from the outflow opening to the scanning spot under the influence of viscous forces exerted on the liquid as a result of the movement of the substrate with respect to the lens system. In the device in accordance with the invention, the liquid supply means is situated, viewed in the tangential direction with respect to the axis of rotation of the table, upstream from the optical axis of the lens system, because the direction wherein the substrate is displaced with respect to the lens system is substantially determined by the direction of rotation of the table. As the outflow opening is arranged directly adjacent the lens of the lens system facing the photosensitive layer, the liquid supplied is transported directly and substantially exclusively to the gap between the photosensitive layer and said lens. As a result, not the whole photosensitive layer has to be provided with liquid, but only a comparatively small part that is situated directly below the lens system. This leads to a substantial reduction of the quantity of liquid to be supplied. As the above-mentioned wall, wherein the outflow opening is formed, extends substantially in an imaginary plane wherein also the side of the lens facing the photosensitive layer extends, said wall substantially blends with said side of the lens. This results, if additionally the liquid is supplied at a sufficient flow rate and at sufficient pressure via the outflow opening, in a homogeneous Couette flow, i.e. a homogeneous liquid film without air inclusions having a linear speed profile, in the gap between the photosensitive layer and the lens. Said homogeneous Couette flow exerts a substantially constant force on the lens system, as a result of which undesirable vibrations of the lens system are precluded as much as possible.
A particular embodiment of a method in accordance with the invention for the manufacture of an optically scannable information carrier, and a particular embodiment of a method in accordance with the invention for the manufacture of a master mold are characterized in that the substrate is disc-shaped and rotated about an axis of rotation which extends perpendicularly to the substrate, while the lens system is displaced substantially in a radial direction with respect to the axis of rotation, the liquid being provided via an outflow opening which, viewed in a tangential direction with respect to the axis of rotation, is upstream from the scanning spot. In these particular embodiments, the substrate is rotated at a comparatively high speed about the axis of rotation, and the lens system is displaced at a comparatively low speed in the radial direction, so that a spiral-shaped track of irradiated and non-irradiated elements is formed on the photosensitive layer. The displacement direction of the substrate at the location of the scanning spot relative to the lens system, is substantially determined by the direction of rotation of the substrate. As the outflow opening, viewed in the tangential direction with respect to the axis of rotation, is upstream from the scanning spot, the liquid is transported, under the influence of the rotation of the substrate, from the outflow opening to the scanning spot which, viewed in the tangential direction, is situated downstream.
A particular embodiment of a method in accordance with the invention for the manufacture of an optically scannable information carrier, and a particular embodiment of a method in accordance with the invention for the manufacture of a master mold are characterized in that the liquid is provided via the outflow opening at a flow rate xcfx86=0.5xc3x97Vxc3x97Hxc3x97W, where W is at least equal to 2xc3x97Hxc3x97NA/{square root over ((n2xe2x88x92NA2))}, and where V is a velocity at which the substrate is displaced at the location of the scanning spot with respect to the lens system, H is a height dimension of the gap, W is a width over which the liquid, viewed in a direction perpendicular to the displacement direction, is spread into the gap, NA is a numerical aperture of the lens system, and n is an optical refractive index of the liquid.
A particular embodiment of a device in accordance with the invention is characterized in that a liquid flow provided, in operation, in the gap via the outflow opening has a flow rate xcfx86=0.5xc3x97Vxc3x97Hxc3x97W, where W is at least equal to 2xc3x97Hxc3x97NA/{square root over ((n2xe2x88x92NA2))}, and where V is a velocity of the substrate at the location of the optical axis with respect to the lens system, H is a height dimension of the gap, W is a width of the liquid flow, viewed in the radial direction, NA is a numerical aperture of the lens system, and n is an optical refractive index of the liquid.
The above-mentioned flow rate is necessary to obtain a homogeneous Couette flow in the gap without air inclusions and having a linear speed profile and a width W. By virtue of the fact that the width W of the liquid flow in the gap has at least the above-mentioned value, an optically effective portion of the lens, situated around the optical axis, is covered entirely with the liquid.
A particular embodiment of a method in accordance with the invention for the manufacture of an optically scannable information carrier, a particular embodiment of a method in accordance with the invention for the manufacture of a master mold, and a particular embodiment of a device in accordance with the invention are characterized in that the width W is at most approximately 10xc3x97H. If W is approximately 10xc3x97H, then the width of the liquid flow in the gap is approximately 2 to 3 times the above-mentioned minimally required width if water is used as the liquid and at customary values of the numerical aperture of the lens system. In this manner, the width of the liquid flow has a margin, so that the optically effective portion of the lens remains wholly covered with liquid also if, in operation, small deviations occur in the flow rate or in the direction of the liquid flow.
A particular embodiment of a method in accordance with the invention for the manufacture of an optically scannable information carrier, a particular embodiment of a method in accordance with the invention for the manufacture of a master mold, and a particular embodiment of a device in accordance with the invention are characterized in that the height H is at least approximately 4 xcexcm and at most approximately 100 xcexcm. It has been found that the methods and the device in accordance with the invention yield satisfactory results if the height H has a value which lies in the above-mentioned range. If the height H is smaller than 4 xcexcm, there is a considerable risk of mechanical contact between the lens system and the substrate. If the height H exceeds 100 82 m, the necessary flow rate of the liquid flow in the gap is so high that there is a considerable risk of mechanical vibrations of the lens system and/or the substrate.
A particular embodiment of a method in accordance with the invention for the manufacture of an optically scannable information carrier, a particular embodiment of a method in accordance with the invention for the manufacture of a master mold, and a particular embodiment of a device in accordance with the invention are characterized in that the height H is at least approximately 7 xcexcm and at most approximately 10 xcexcm. It has been found that the methods and the device in accordance with the invention yield optimum results if the height H has a value in the above-mentioned range.
A particular embodiment of a method in accordance with the invention for the manufacture of an optically scannable information carrier, a particular embodiment of a method in accordance with the invention for the manufacture of a master mold, and a particular embodiment of a device in accordance with the invention are characterized in that the outflow opening is round and its diameter is at most approximately 0.5xc3x97W. To preclude air inclusions in the liquid flow in the gap, a predetermined, minimum outflow pressure of the liquid flow in the outflow opening is required. At a predetermined flow rate of the liquid flow, the outflow pressure decreases as the outflow opening increases, so that the risk of air inclusions increases as the outflow opening is larger. It has been found that the risk of air inclusions is negligibly small if the outflow opening is round with a diameter which is at most equal to approximately 0.5xc3x97W.
A particular embodiment of a device in accordance with the invention is characterized in that the side of the lens facing the photosensitive layer is provided with a dam which, viewed in the tangential direction, extends upstream from the optical axis and has a width which is equal to a desired width W of the liquid flow, while the outflow opening is provided in a further dam, which has the same width and, viewed in the tangential direction, connects to the dam of the lens. In this particular embodiment of the device in accordance with the invention, the wall having the outflow opening is formed by a side of said further dam, which side faces the photosensitive layer. The liquid flow present in the gap between the dam, the further dam and the photosensitive layer is retained in the gap, viewed at right angles to the flow direction, under the influence of capillary liquid forces. As a result, at a sufficiently high flow rate of the liquid flow, the dam and the further dam accurately determine the width and the position of said liquid flow, so that only a comparatively small margin with respect to the minimally required width of the liquid flow is necessary to always cover, in operation, the optically effective portion of the lens with liquid. In addition, in this particular embodiment, the varying forces exerted by the liquid flow on the lens system are further reduced.
A particular embodiment of a method in accordance with the invention for the manufacture of an optically scannable information carrier, and a particular embodiment of a method in accordance with the invention for the manufacture of a master mold are characterized in that the liquid is extracted from the photosensitive layer, viewed in the displacement direction, downstream from the lens system.
A particular embodiment of a device in accordance with the invention is characterized in that the device comprises an extraction device which is arranged downstream, viewed with respect to the outflow opening and the lens system. As the liquid is extracted from the photosensitive layer downstream from the lens system, it is substantially precluded that liquid that has already been used is re-introduced into the gap and disturbs the liquid flow in the gap that is supplied via the outflow opening.
A particular embodiment of a device in accordance with the invention is characterized in that the extraction device has an extraction mouth which can be displaced, by means of a further displacement device, synchronously with the lens system in a further radial direction with respect to the axis of rotation. The extraction mouth is displaced by means of the further displacement device in such a way that, in operation, the extraction mouth is always situated at a distance from the axis of rotation which corresponds to a distance between the lens system and the axis of rotation. In this manner, a practical structure of the extraction device is obtained, and the extraction mouth has minimum dimensions.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.